1. Field of the Invention
The present invention relates to a memory device for recording 9-bit length video data preferred when used for reproducing video data at variable speeds in for example a video server device.
2. Description of the Related Art
Along with the advances in recording technology and image processing technology, A/V server devices which encode large amounts of video data and record them in a randomly accessible recording medium to enable the data to be easily and efficiently edited and transmitted.
One of most basic functions in such an A/V server device is the variable speed reproduction of video data. This is utilized for various purposes such as editing, viewing, and confirmation of video data. Usually, variable speed reproduction is carried out by writing the decoded reproduction video signal in a memory in units of frames and reading and reproducing any of the data in the memory in units of fields in accordance with the reproduction speed.
At this time, the data which is written into and read out from the memory is a total 9-bit length data comprised of the main 8-bit video data and a CFI signal, that is, a 1-bit serial signal which has color frame information of this video data and which is transmitted together with the main video data between principal ICs for processing.
The reason why the CFI signal is necessary in addition to the main video data as the data written into and read out from the memory at the time of such variable speed reproduction will be explained next.
In the video signal, the start point of the valid picture is different between the first field comprising one picture, that is, one frame, and the second field. When taking note of the vertical time direction of this, there is a deviation of one line.
In standard speed normal reproduction, smooth pictures are reproduced by sequentially and regularly outputting the picture of the first field at the timing at which the picture of the first field should be output and then the picture of the second field at the timing at which the picture of the second field should be output.
At the time of variable speed reproduction, however, the data is reproduced in units of fields (field reproduction), so the pictures of the first field and the second field are not always sequentially and regularly output as in standard speed reproduction. That is, it is necessary to output the picture of the second field at the timing at which the picture of the first field should be output and, conversely, output the picture of the first field at the timing at which the picture of the second field should be output.
If the data were to be output without any processing at this time, since, as explained above, there is a deviation of one line in the start points of the pictures in the vertical time direction between the first field and the second field, this amount of shimmy will occur in the vertical direction in the output pictures.
The CFI signal includes, other than the color frame information of the main video data, information indicating the first field or second field (CF0). Therefore, by transmitting this CFI signal together with the video data to the principal ICs, it becomes possible for each IC to carry out the required processing for outputting smooth pictures based on this information.
In general, however, the data which is input and output in a memory IC generally consists of 8 to 16 bits. For this reason, when, as in the memory device explained above, the data to be written into or read out from the memory consists of 9 bits, the video data cannot be efficiently recorded. Namely, when such a memory is used, the input or output of the data requires either use of two 8-bit memory ICs or one 16-bit memory IC. In either case, the remaining 7 bits worth of memory space becomes wasted, so there was a disadvantage of expensive cost. Further, the number of memory ICs used is increased in comparison with the required storage capacity, so there also existed the disadvantage of the increase of size of the device.